Tissue sections are commonly examined by microscopic examination, for both research and clinical diagnostic purposes. Thin tissue sections or cellular preparations are commonly 1-10 microns thick, and are nearly transparent if untreated. In order to visualize various histologic features, a wide array of staining procedures have been developed over the years that highlight various cellular or extracellular components of the tissues. Histochemical stains, also commonly termed "special stains," employ chemical reactions to color various chemical moieties. Immunohistochemical stains employ antibodies as probes to color specific proteins, commonly via enzymatic deposition of a colored precipitate. Each of these histochemical and immunohistochemical stains requires the addition and removal of reagents in a defined sequence for specific time periods. Therefore, a need arises for a slide stainer that can perform a diversity of stains simultaneously under computer control, as specified by the technologist.
Some of these histochemical and immunohistochemical stains employ reagents that may be toxic, carcinogenic, or immiscible in water. Because of increasingly stringent local waste disposal requirements, many laboratories must now pay to dispose of these wastes through special, hazardous, waste disposal companies. It is therefore desirable to minimize the volume of waste liquid that has to be treated as hazardous waste. With the advent of modern, sophisticated, slide staining automation, it is therefore desirable to incorporate features into an instrument to accomplish that task.
A common method for removing waste liquids from the surface of a slide is to flush or blow it off the surface of a slide into a common catch basin. A representative example of such an approach is that described in U.S. Pat. No. 5,595,707. In that embodiment, reagent is removed from the slide by either blowing with a gas stream or flushing with a liquid reagent. Liquid falls off the slide into a catch basin. A similar approach (using a common catch basin for all liquid waste) is taken in several other slide stainers, described in U.S. Pat. Nos. 5,425,918 and 5,231,029, and that of Stark, E., et. al. 1988, An automated device for immunocytochemistry, J. Immunol. Methods 107:89-92.
A similar design approach is evidenced by the slide stainer marketed by BioGenex Corporation, described in U.S. Pat. No. 5,439,649. It uses a similar catch basin for collecting liquid waste. This design approach causes the entire catch basin to become contaminated. The disadvantage of this approach is that the contaminated or toxic liquid is spread over a larger surface area than the slide itself, as it is caught in a basin. In order to ensure that the next waste liquid will not contain residual amounts of the toxic material, the catch basin must be flushed with a larger volume of wash solution. This results in an increased volume of toxic liquid waste for special hazardous disposal.
An alternative design approach to handling waste liquids from a slide stainer is described in U.S. Pat. No. 4,543,236. Their invention shows a means for aspirating liquid waste, under force of vacuum, to a common waste bottle. In that invention, liquid waste is aspirated through drain lines permanently connected to each slide-containing vessel. A dedicated valve for each slide-containing vessel opens to allow aspiration of the liquid contents. The system is "closed," in that the liquid supply and waste lines do not become exposed to the atmosphere. An advantage of this approach is that liquid waste is not spread around a large catch basin. However, the drawback of this design is that a dedicated valve and permanent tubing lines are required for each slide-containing vessel. As the number of slides increases, the apparatus becomes expensive and complex to assemble and repair. This limitation was apparent in their particular embodiment, as the staining apparatus only accommodated five slides.
A conceptually similar approach is described in U.S. Pat. No. 4,358,470, except that in this invention, waste liquids are channeled into their original containers, to be used repetitively. Their invention did not require a large number of distinct procedures to be applied to different microscope slides. Rather, all of the biological specimens, mounted on electron microscopic grids, were held in a common chamber and treated in an identical manner. With only a single incubation chamber, permanently closed plumbing lines for liquid supply and waste was a reasonable, cost-efficient, design. It would not be applicable to situations where numerous slides are to be stained using different chemical staining procedures.
A third method of automated slide staining for immunohistochemistry was described by Brigati, U.S. Pat. No. 4,731,335. In that invention, liquid was applied to and removed from capillary gaps that were formed by two slides closely apposed together. To remove the liquid, the edges of the slides were abutted against absorbent towels, causing the liquid to be adsorbed. Therefore, waste liquid was in a solid, adsorbed form.
A fourth method for rinsing slides has been to simply dip the slides containing a reagent into a vat of liquid, such as water or buffer. The reagent dilutes out in the excess volume of liquid wash solution, preparing the slide for treatment with the next reagent that is scheduled to be applied. An example of that approach is the slide stainer described in U.S. Pat. No. 4,092,952. A similar (dipping of slides into a vat) approach, specially tailored for immunohistochemistry, is described in a publication by Muir and Alexander, 1987, Easier immunoperoxidase staining with labour saving incubator box. J Cain Pathol 40:348-50.
A previous invention by one of the present inventors, U.S. Pat. Nos. 4,847,208 and 5,073,504, disclosed a means for aspirating liquids from the surface of slides. A pipette is manually lowered until it is in contact with the wetted slide surface. Liquid was aspirated into a single waste bottle by vacuum force.